1. Field of the Invention
The present invention relates to an improvement in a glass quenching apparatus for quenching a heated glass sheet to manufacture tempered glass.
2. Description of Related Art
FIG. 14 hereof diagrammatically illustrates a conventional glass manufacturing method which is designed to manufacture tempered glass sheets of a thickness in the range of 3 mm to 5 mm. In general, such glass sheets of a 3 mm to 5 mm thickness are called normal-thickness glass sheets.
In the glass manufacturing method of FIG. 14, air jets 102 are emitted upward from a floating bed 101 within a heating furnace 100 so that a glass sheet 104 is floated above the floating bed 101 by the pressure of air jets, and the floated glass sheet 104 is heated to a predetermined temperature higher than its softening point or temperature while it is transferred as indicated by a profiled arrow.
Then, the heated glass sheet 104 is delivered from the heating furnace 100 to a glass quenching station 106, where air 108 is blown onto opposite surfaces of the glass sheet 104 to thereby quench the heated glass sheet 104. With this quenching, a compressive layer is formed in and along the surface of the glass sheet 104, which increases the strength of the glass sheet 104.
Subsequently, the thus-quenched or tempered glass sheet 104 is conveyed to a next station by a bed of rollers 109.
As is known in the art, the quenched glass sheet has an increased strength by virtue of a compressive layer formed in and along its surface by rapidly cooling, i.e., quenching, the surface of a glass sheet heated up to a predetermined temperature to thereby produce a temperature difference between the surface and interior of the glass sheet. Thus, a glass sheet having a smaller thickness, such as 1.5 mmxe2x88x923.0 mm, than that of the normal-thickness glass sheet (hereinafter referred to as xe2x80x9csmall-thickness glass sheetxe2x80x9d) is cooled in the interior more readily than the normal-thickness glass sheet.
Accordingly, for such small-thickness glass sheets, it is necessary to quench their surface within an even shorter time than for the normal-thickness glass sheets.
One example of the conventionally-known methods for quenching the small-thickness glass sheets is shown in Japanese Patent Publication No. HEI 6-24995 under the title of xe2x80x9cMethod of Manufacturing Tempered Glass Sheetsxe2x80x9d. According to the disclosed method, a small-thickness glass sheet is quenched within a short time period by a combined use of compressor air and blower air. Specifically, the air supplied from the compressor (compressor air) is rapidly decompressed in a nozzle to produce a shock wave, so that the compressor air with the shock wave produced therein is blown onto the small-thickness glass sheet and simultaneously the air supplied from the blower (blower air) is blown onto the small-thickness glass sheet to thereby quench the glass sheet.
With the known quenching methods, however, various inconveniences are encountered when small-thickness glass sheets of different sizes are to be quenched, as set forth below in relation to a case where small-thickness glass sheets of two different sizes are each formed into a curved tempered glass sheet.
FIGS. 15A and 15B are schematic views explanatory of basic operating principles of a conventionally-known glass quenching apparatus. More specifically, FIG. 15A illustrates an example where a small-thickness glass sheet 110 of a relatively large size (width W1) is quenched, and FIG. 15B illustrates an example where a small-thickness glass sheet 120 of a relatively small size (width W2) is quenched.
In the example shown in FIG. 15A, air jets are emitted upward from a floating bed 109 of the glass quenching apparatus so that the small-thickness and large-size glass sheet 110 previously curved at a preceding stage is floated above the floating bed 109 by the pressure of air jets. Then, the floated glass sheet 110 is retained at one edge (right edge in FIG. 15A) 110a by a holder 112 of a transfer arm 111. During emission of the air jets from the floating bed 109, air is jetted downward through a plurality of nozzles 113.
Under these conditions, a conveyor chain 114 is driven to move the glass sheet 110, via the transfer arm 111, in a direction normal to the plane of the sheet of FIG. 15A, so that the glass sheet 110 is quenched during the movement by the chain 114.
It is also generally known that a central region of glass sheets is hard to cool while edge regions of glass sheets are easy to cool. Because of this physical principle, there is a need to enhance the cooling capability of the quenching apparatus at a position P1 corresponding to a central region 110b of the small-thickness and large-size glass sheet 110. The terms xe2x80x9ccooling capabilityxe2x80x9d refer to a degree at which the heat of the heated glass can be absorbed by the air jets. Namely, the greater cooling capability can quench the glass sheet within a shorter time.
In the example shown in FIG. 15B, similarly to the example of FIG. 15A, the small-thickness and small-size glass sheet 120 previously curved at the preceding stage is retained at its right edge 120a in this figure by the holder 112 of the conveyor chain 114 and moved by the conveyor chain 114 via the transfer arm 111 in the direction normal to the plane of the sheet of FIG. 15B, so that the glass sheet 120 is quenched during the movement by the chain 114. Because a central region 120b of the glass sheet 120 is hard to cool as compared to the sheet edge portions, there is a need to enhance the cooling capability of the quenching apparatus at a position P2 corresponding to the central region 120b of the small-thickness and small-size glass sheet 120. Because, in this example, the glass sheet 120 is set on the floating bed 109 with its right edge 120b used as a positional reference and then moved in the direction normal to the plane of the sheet of the figure while being maintained in this positional condition, tile central region 120b of the small-size glass sheet 120 is displaced rightward from the central region 110b of the large-size glass sheet 110.
Namely, the glass quenching apparatus shown in FIGS. 15A and 15B is designed to quench each of the small-thickness glass sheets 110 and 120 by retaining the reference edge (right edge) 110a or 120a of the glass sheet via the holder 112 to support the glass sheet in a predetermined place above the floating bed 109, i.e., by setting the glass sheet on an edge-guided basis. Because the glass sheets 110 and 120 of two different (large and small) sizes are set on such an edge-guided basis, the respective central regions of the sheets 110 and 120 would be significantly displaced from each other above the floating bed 109, so that there arises a need for the quenching apparatus to have increased cooling capabilities at two positions P1 and P2. This means that for use with three or more different sizes of glass sheets, the quenching apparatus needs to have increased cooling capabilities at three or more separate portions.
Accordingly, the conventional glass quenching apparatus of the foregoing construction requires a high equipment cost, which increases the cost of tempered glass sheets.
Additionally, the conventional glass quenching apparatus, when used for quenching small-thickness glass sheets, induces an increase in manufacturing cost because a large quantity of air is wasted for quenching other regions of the small-thickness glass sheets than the central region.
It is therefore an object of the present invention to provide a glass quenching apparatus which is capable of quenching tempered glass sheets without increasing the cost of the tempered glass sheets.
To achieve the foregoing object, the present invention provides a glass quenching apparatus for quenching a glass sheet heated to a predetermined temperature, comprising: a first nozzle group for jetting blower air onto opposite surfaces of the glass sheet, the first nozzle group being comprised of stationary nozzles; and a second nozzle group for jetting compressor air onto at least one of the opposite surfaces of the glass sheet, the second nozzle group being comprised of movable nozzles which are capable of moving parallel to a plane of the glass sheet.
Since the second nozzle group is movable, it can be located at an optimum position with respect to a desired region (namely, hard-to-cool portion) of any of glass sheets of different sizes. The hard-to-cool portions of the glass sheets can, therefore, be quenched under optimum conditions. The remaining region or portion of the glass sheets is quenched by the first nozzle group under optimum conditions. Thus, merely by adding the second nozzle group, quenching of the respective hard-to-cool portions of the various small-thickness glass sheets can be achieved. The equipment cost of the glass quenching apparatus is relatively low. Additionally, since the movable second nozzle group is able to focus the compressor air onto the desired region (hard-to-cool portion) of the small-thickness glass sheet, compressor air can be used efficiently without loss.
The glass quenching apparatus may further include a nozzle moving device for moving the second nozzle group in both a first direction transverse to a direction of movement of the glass sheet, and a second direction perpendicular to the plane of the glass sheet.
The nozzle moving device enables accurate positioning of the second nozzle group relative to the desired region (hard-to-cool portion) of any of the glass sheets of different sizes. To improve the positioning accuracy, the apparatus may further include an adjusting device associated with the nozzle moving device and operative to swing the movable nozzles horizontally and vertically so as to adjust the position of the movable nozzles relative to the desired region of the glass sheet.
The glass quenching apparatus may further include a conveyor means or unit for horizontally conveying the glass sheet using a pusher arm while the glass sheet is held in a floating condition by the pressure of blower air.
By thus conveying the glass sheet, if the second nozzle group is held stationarily at a predetermined position, air jets issued from the second nozzle group will impinge on a region or portion of the glass sheet extending continuously from a front edge to a rear edge of the glass sheet.
In the case where edge portions of a glass sheet are hard to cool due to heat transmitted directly from the arms of the conveyor unit being in contact with the glass sheet edges, the second nozzle group may be displaced to a position aligned with a path of movement of the edge portions of the glass sheet. The edge portions can be quenched by air jets issued from the second nozzle group.